The elections in Chon Buri are being closely watched because not only is it a battleground between two opposing camps, but the outcome can also decide the fate of Prime Minister Prayut Chan-o-cha, who is seeking to return as head of the government.
The race will be a test of strength between two rival factions that recently walked away from the ruling Palang Pracharath Party (PPRP).
One is led by Sonthaya Khunplome, heir of the influential family that has dominated politics for decades due to the influence of the late Somchai Khunplome, better known as Kamnan Poh, and the other headed by Suchart Chomklin, the PPRP's former director who was once under the family's wing.
Mr Suchart was a successful local politician who switched to national politics in 2011 and won under the banner of Palang Chon Party led by Mr Sonthaya.
He joined the PPRP to contest the 2019 polls, and together with his team won three seats for the party.
He recently defected to the United Thai Nations (UTN) Party, in which Gen Prayut serves as the chief strategist.
He is assigned to spearhead the party's election campaign in Chon Buri and the eastern region.
Mr Sonthaya also left the PPRP to reunite with the Pheu Thai Party to take charge of the party's elections in the east.
Both rival camps will battle for their share of House seats, which increases from eight to 10 in the upcoming polls. Both UTN and Pheu Thai aim for nothing but a clean sweep of 10 seats.
Chon Buri is a key province for the UTN Party, which has been recruiting candidates to guarantee it will take home at least 25 seats -- a minimum required by the constitution for a party to nominate a prime minister candidate for a vote in parliament.
Some reports suggest Gen Prayut is dragging his feet over a House dissolution because the UTN is not ready for the elections, and it will not be ready until it can guarantee a win of 25 House seats.
The UTN is counting on Mr Suchart to make a clean sweep in this eastern province.
Suchart Chomklin
Pheu Thai, meanwhile, is also banking on the Khunplome family to help the party secure a "landslide victory" and put a stop to Gen Prayut's return.
However, Pheu Thai's hopes of winning all 10 seats took a blow when Culture Minister Itthipol Khunplome, younger brother of Mr Sonthaya, said he would not join Pheu Thai and is considering his future.
That is a clear sign of a rift in the Khunplome group, and a hint that some of its members doubt Pheu Thai will win via a landslide.
The Chon Buri election is predicted to be one of the most competitive contests, with analysts saying that rivals will mobilise their resources and may resort to "money politics" to achieve their goal.
However, they reckon that clean sweeps will be difficult to produce.
The 10 seats will be split between UTN and Pheu Thai while the Move Forward Party (MFP), which won three seats in the 2019 polls, may get a few seats if rival candidates undercut each other.
Fierce battleground
Sakda Noppasit, the Move Forward Party's coordinator for election candidates, said the outcome of the elections in this eastern province is anything but certain and there will be no such thing as a landslide win here.
He said the Khunplome group and Mr Suchart's Palang Mai group are predicted to capture two seats each in their strongholds, while the remaining four seats will be fiercely fought over.
Without Mr Sonthaya, the PPRP, which won five seats out of eight in the 2019 elections, may have a hard time retaining support in some constituencies, he noted.
According to Mr Sakda, the MFP candidates, considered underdogs in the upcoming polls, have a shot and may grab a few seats if the candidates from these three rival groups undercut each other.
A source familiar with political canvassing in Chon Buri said the elections will be a two-horse race between the Pheu Thai Party and the UTN Party.
While the MFP is predicted to gather votes in urban areas, that won't be enough to secure a win, the source said.
The source also brushed off speculation that the candidates from the PPRP and the UTN could win because Chon Buri, which houses army and naval barracks, has large numbers of troops.
"It won't make a difference unless there are specific instructions about votes," said the source.
According to the source, Pheu Thai with Mr Sonthaya as its flagbearer is predicted to take six to seven seats while the UTN is forecast to win three to four seats.
If a camp led by Sarawuth Nuengchamnong, PPRP MP from Chon Buri, switches to Pheu Thai, the PPPR will be left with no seat, the source added.
Thirin Thanyawattanakul, president of Chon Buri's chamber of commerce, said no matter which party wins, it is unlikely to affect the province in terms of policy changes.
He also said it is too early to say who will win the elections because Pheu Thai and Gen Prayut have their support bases here.
However, while most expect a two-horse race between the Pheu Thai and the UTN, other parties cannot be ruled out if they have policies that appeal to voters.
Old clique vs new force
Olarn Tinbangtiew, a lecturer at the faculty of political science and law, Burapha University, said that on the surface the election in Chon Buri is a battle between major parties.
In fact, it is a showdown between the Khunplome clan and the Palang Mai group.
He said stakes are high for both sides who need a decisive victory in this eastern province, which was once seen as the impregnable stronghold of the Khunplome faction.
"The Khunplome family and Pheu Thai need each other to win in this province. Mr Suchart is aware of a political shift and he has accumulated resources for the election," the lecturer said.
The academic said Mr Sonthaya's family still retains the influence amid changes in politics while Mr Suchart may count on support from the politicians who were ditched by Pheu Thai, so he reckoned the 10 House seats will be split by the two.
But the door is not entirely closed for the MFP, which is expected to receive sizeable support from urban voters, especially in Pattaya, Bang Lamung, Na Kluea and some parts of Sri Racha, where residents have relocated from other provinces, he said.
"Chon Buri was once the capital of yellow-shirts who were against the Thaksin regime.
"That sentiment remains and I believe it will be used in the elections. That's why the Khunplome family tries to focus on economic development," he said.
Mr Sonthaya, however, said his team's "rivals" are the problems which people in Chon Buri face and its focus is how to tackle them.
"We're not focusing on parties or their candidates. We want to show the people how the Pheu Thai Party will approach solving their problems," he said.
Mr Sonthaya said the candidates are ready to fight in every constituency but refused to discuss the target.
"If I say I expect to win half of the seats, it'll be too low. But I really don't want to talk about the target.
"It's the people who decide. If they like what they hear, they will choose," Mr Sonthaya said.